The present invention relates generally to sealing plugs for lead batteries, and more particularly, to a sealing plug including a microporous frit and a pressure-release valve in a housing for enclosing the electrolyte filling openings of the battery's cell lid.
Under certain operating conditions, such as during recharging, sealing plugs are used to ensure the safe escape of gases from the battery. In such cases, the sealing plug functions as a ventilating seal. Frequently, the sealing plug includes safety devices which operate both individually and in combination with one another to prevent damage resulting from the uncontrolled release of cell gases.
Various devices have been proposed in an effort to ensure safe battery operation. For example, pressure-releasing valves of various designs have been used which open only upon reaching an impermissibly high internal pressure. Porous frits of glass or ceramic have been used to enclose the gas ventilating opening and shield the explosive oxyhydrogen gas mixture in the interior of the battery from ignition by exposure to external sparks (so-called "flashback"), forming a sparkover ignition barrier. Catalysts have been used for recombination of the cell gases, and anti-splash baskets or devices for separating acid drops from the gas stream have been proposed.
For example, DE-OS 22 08 858 discloses a simple sealing plug equipped with a pressed-on, disk-shaped blocking member formed of a gas-permeable, but essentially liquid impermeable material. DE-PS 24 02 718 discloses a sealing plug having a porous barrier preceded by horizontal plates with openings which force the cell gases into a winding (serpentine) flow path. German Utility Model G 91 04 291 discloses the combination of a pressure-release valve and a frit body in a sealing plug.
A gas containing an acid mist can escape not only from lead batteries with liquid electrolytes, but also from those with gelled electrolytes. This is caused by "syneresis", a spontaneous contraction occurring predominantly in the head space of the cell with the precipitation of liquid from the acid gel during aging. This effect intensifies, especially in the case of horizontally constructed cells, so that upon the opening of the pressure-release valve, an acid mist passes to the exterior.
A disadvantage of the foregoing is that the discharged acid mist then tends to precipitate as drops on the cell lid. This is objectionable for maintenance personnel, and the acid mists which are produced can cause the overall function of the plug to be impaired.